The statistical association of rotavirus- and enterotoxigenic Escherichia coli-specific serum antibody with demographic and hygienic factors was tested in Ecuadorian children enrolled in a cross-sectional survey. In 7- to 10-month-old children, enterotoxigenic E. coli-specific antibody was associated (P less than 0.05) with poor drinking water quality, lack of a sewage system, and feeding of supplementary food. In 7- to 14-month-old children, rotavirus-specific antibody was associated only with family size but notably not with hygienic factors.